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| Nanomaterials arranged on a chip before being cut into their final forms at the SLAC National Accelerator Laboratory in Menlo Park, Calif. Matt Beardsley/SLAC |
Not long after Gordon E. Moore proposed in 1965 that the number of transistors that could be etched on a silicon chip would continue to double approximately every 18 months, critics began predicting that the era of “Moore’s Law” would draw to a close.
More than ever recently, industry pundits have been warning that the progress of the semiconductor industry is grinding to a halt — and that the theory of Dr. Moore, an Intel co-founder, has run its course.
If so, that will have a dramatic impact on the computer world. The innovation that has led to personal computers, music players and smartphones is directly related to the plunging cost of transistors, which are now braided by the billions onto fingernail slivers of silicon — computer chips — that may sell for as little as a few dollars each.
But Moore’s Law is not dead; it is just evolving, according to more optimistic scientists and engineers. Their contention is that it will be possible to create circuits that are closer to the scale of individual molecules by using a new class of nanomaterials — metals, ceramics, polymeric or composite materials that can be organized from the “bottom up,” rather than the top down.
For instance, semiconductor designers are developing chemical processes that can make it possible to “self assemble” circuits by causing the materials to form patterns of ultrathin wires on a semiconductor wafer. Combining these patterns of nanowires with conventional chip-making techniques, the scientists believe, will lead to a new class of computer chips, keeping Moore’s Law alive while reducing the cost of making chips in the future.
“The key is self assembly,” said Chandrasekhar Narayan, director of science and technology at IBM’s Almaden Research Center in San Jose, Calif. “You use the forces of nature to do your work for you. Brute force doesn’t work any more; you have to work with nature and let things happen by themselves.”
To do this, semiconductor manufacturers will have to move from the silicon era to what might be called the era of computational materials. Researchers here in Silicon Valley, using powerful new supercomputers to simulate their predictions, are leading the way. While semiconductor chips are no longer made here, the new classes of materials being developed in this area are likely to reshape the computing world over the next decade.
“Materials are very important to our human societies,” said Shoucheng Zhang, a Stanford University physicist who recently led a group of researchers to design a tin alloy that has superconductinglike properties at room temperature. “Entire eras are named after materials — the stone age, the iron age and now we have the silicon age. In the past they have been discovered serendipitously. Once we have the power to predict materials, I think it’s transformative.”
Pushing this research forward is economics — specifically, the staggering cost semiconductor manufacturers are expecting to pay for their next-generation factories. In the chip-making industry this has been referred to as “Moore’s Second Law.”
Two years from now new factories for making microprocessor chips will cost from $8 to $10 billion, according to a recent Gartner report — more than twice as much as the current generation. That amount could rise to between $15 and $20 billion by the end of the decade, equivalent to the gross domestic product of a small nation.
The stunning expenditures that soon will be required mean that the risk of error for chip companies is immense. So rather than investing in expensive conventional technologies that might fail, researchers are looking to these new self-assembling materials.
In December, researchers at Sandia National Laboratories in Livermore, Calif., published a Science paper describing advances in a new class of materials called “metal-organic frameworks” or MOFs. These are crystalline ensembles of metal ions and organic molecules. They have been simulated with high-performance computers, and then verified experimentally.
What the scientists have proven is that they can create conductive thin films, which could be used in a range of applications, including photovoltaics, sensors and electronic materials.
The scientists said that they now see paths for moving beyond the conductive materials, toward creating semiconductors as well.
According to Mark D. Allendorf, a Sandia chemist, there are very few things that you can do with conventional semiconductorsto change the behavior of a material. With MOFs he envisions a future in which molecules can be precisely ordered to create materials with specific behaviors.
“One of the reasons that Sandia is well positioned is that we have huge supercomputers,” he said. They have been able to simulate matrixes of 600 atoms, large enough for the computer to serve as an effective test tube.
In November, scientists at the SLAC National Accelerator Laboratory, writing in the journal Physical Review Letters, described a new form of tin that, at only a single molecule thick, has been predicted to conduct electricity with 100 percent efficiency at room temperature. Until now these kinds of efficiencies have only been found in materials known as superconductors, and then only at temperatures near absolute zero.
The material would be an example of a new class of materials called “topological insulators” that are highly conductive along a surface or edge, but insulating on their interior. In this case the researchers have proposed a structure with fluorine atoms added to a single layer of tin atoms.
The scientists, led by Dr. Zhang, named the new material stanene, combining the Latin name for tin — stannum — with the suffix used for graphene, another material based on a sheet of carbon atoms a single molecule thick.
The promise of such a material is that it might be easily used in conjunction with today’s chip-making processes to both increase the speed and lower the power consumption of future generations of semiconductors.
The theoretical prediction of the material must still be verified, and Dr. Zhang said that research is now taking place in Germany and China, as well as a laboratory at U.C.L.A.
It is quite possible that the computational materials revolution may offer a path toward cheaper technologies for the next generation of computer chips.
That is IBM’s bet. The company is now experimenting with exotic polymers that automatically form into an ultrafine web and can be used to form circuit patterns onto silicon wafers.
Dr. Narayan is cautiously optimistic, saying there is a good chance that bottoms-up self-assembly techniques will eliminate the need to invest in new lithographic machines, costing $500 million, that use X-rays to etch smaller circuits. .
“The answer is possibly yes,” he said, in describing a lower cost path to denser computer chips.
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